Constant viscosity elastic fluid

Last updated

Constant viscosity elastic liquids, also known as Boger fluids are elastic fluids with constant viscosity. This creates an effect in the fluid where it flows like a liquid, yet behaves like an elastic solid when stretched out. Most elastic fluids exhibit shear thinning (viscosity decreases as shear strain is applied), because they are solutions containing polymers. But Boger fluids are exceptions since they are highly dilute solutions, so dilute that shear thinning caused by the polymers can be ignored. Boger fluids are made primarily by adding a small amount of polymer to a Newtonian fluid with a high viscosity, a typical solution being polyacrylamide mixed with corn syrup. It is a simple compound to synthesize but important to the study of rheology because elastic effects and shear effects can be clearly distinguished in experiments using Boger fluids. Without Boger fluids, it was difficult to determine if a non-Newtonian effect was caused by elasticity, shear thinning, or both; non-Newtonian flow caused by elasticity was rarely identifiable. Since Boger fluids can have constant viscosity, an experiment can be done where the results of the flow rates of a Boger liquid and a Newtonian liquid with the same viscosity can be compared, and the difference in the flow rates would show the change caused by the elasticity of the Boger liquid. [1]

Contents

Research

Original Boger fluid

Boger fluids are named after David V. Boger, who in the late 1970s was the primary researcher pushing for the study of constant viscosity elastic liquids. [2] He released his first paper on Boger fluids in 1977, titled "A Highly Elastic Constant-Viscosity Fluid", where he described the ideal fluid for experimentation as a fluid that is "highly viscous and highly elastic at room temperature and at the same time is optically clear". The main purpose of the paper was to experiment on the highly viscous and highly elastic fluid and record the fundamental rheometric properties of the fluid. Such a fluid would allow for experimentation under conditions not affected by inertia and shear thinning effects, and influence of inertia would easily be distinguishable. [3]

He began his research using maltose syrups (corn syrups) mixed with a small amount of water. He then tested shear stress versus shear rate of the solution to prove that the solution was a Newtonian fluid. This was done by using a R16 Weissenberg rheogoniometer [4] (a rheogoniometer calibrated to measure specifically the behavior of a viscoelastic polymer solution) for the low range shear stress rates, and the high rates were measured using a capillary rheometer, a device used to measure shear stress rates under high stress. The data proved that there was a linear relationship between shear stress and shear rate with the slope being very close to one, meaning the maltose syrup was indeed a Newtonian fluid. Once 0.08% of the polymer polyacrylamide was added, the flow properties drastically changed. Elastic properties were introduced to the fluid while only a slight amount of shear thinning was observed, small enough to be ignored. The syrup solution had properties very similar to a polymer melt, but there was no shear thinning and the materials could be produced at room temperature.

Subsequent Boger fluids

The original Boger fluid was an aqueous solution, as were all the solutions synthesized until 1983, when organic Boger fluids were produced using a dilute solution of polyisobutylene (PIB) in a mixture of polybutene (PB) with a small quantity of kerosene oil added. From then on, most Boger fluids have been PIB - PB solutions. Other recipes include:

Commercial use

Waste disposal

The best application so far for Boger fluids is solving the problem of disposal for the waste produced in the processing of bauxite to alumina for use in producing aluminium, and there is normally two or three times more "red mud" produced than alumina. Normally, the waste, known as "red mud", was disposed of by being flushed down dams with millions of liters of water. The dams continue to hold the "red mud", because it does not work as a building foundation and also can't be used as farm land. Companies needed to find a way to efficiently dispose of it all onto the dams without clogging the tubes it was being transferred in. With the development of Boger fluids, aluminum giant Alcoa developed a way to convert the waste into a thick matter that could still flow down pipes. Using this method, the dangers of tubes erupting was cut out, leading to a more sustainable practice. [5]

Related Research Articles

Rheology is the study of the flow of matter, primarily in a fluid state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force. Rheology is a branch of physics, and it is the science that deals with the deformation and flow of materials, both solids and liquids.

A viscometer is an instrument used to measure the viscosity of a fluid. For liquids with viscosities which vary with flow conditions, an instrument called a rheometer is used. Thus, a rheometer can be considered as a special type of viscometer. Viscometers can measure only constant viscosity, that is, viscosity that does not change with flow conditions.

A non-Newtonian fluid is a fluid that does not follow Newton's law of viscosity, that is, it has variable viscosity dependent on stress. In non-Newtonian fluids, viscosity can change when under force to either more liquid or more solid. Ketchup, for example, becomes runnier when shaken and is thus a non-Newtonian fluid. Many salt solutions and molten polymers are non-Newtonian fluids, as are many commonly found substances such as custard, toothpaste, starch suspensions, corn starch, paint, blood, melted butter, and shampoo.

The Deborah number (De) is a dimensionless number, often used in rheology to characterize the fluidity of materials under specific flow conditions. It quantifies the observation that given enough time even a solid-like material might flow, or a fluid-like material can act solid when it is deformed rapidly enough. Materials that have low relaxation times flow easily and as such show relatively rapid stress decay.

A Newtonian fluid is a fluid in which the viscous stresses arising from its flow are at every point linearly correlated to the local strain rate — the rate of change of its deformation over time. Stresses are proportional to the rate of change of the fluid's velocity vector.

<span class="mw-page-title-main">Shear stress</span> Component of stress coplanar with a material cross section

Shear stress is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. Normal stress, on the other hand, arises from the force vector component perpendicular to the material cross section on which it acts.

In continuum mechanics, a power-law fluid, or the Ostwald–de Waele relationship, is a type of generalized Newtonian fluid for which the shear stress, τ, is given by

<span class="mw-page-title-main">Bingham plastic</span> Material which is solid at low stress but becomes viscous at high stress

In materials science, a Bingham plastic is a viscoplastic material that behaves as a rigid body at low stresses but flows as a viscous fluid at high stress. It is named after Eugene C. Bingham who proposed its mathematical form.

Hemorheology, also spelled haemorheology, or blood rheology, is the study of flow properties of blood and its elements of plasma and cells. Proper tissue perfusion can occur only when blood's rheological properties are within certain levels. Alterations of these properties play significant roles in disease processes. Blood viscosity is determined by plasma viscosity, hematocrit and mechanical properties of red blood cells. Red blood cells have unique mechanical behavior, which can be discussed under the terms erythrocyte deformability and erythrocyte aggregation. Because of that, blood behaves as a non-Newtonian fluid. As such, the viscosity of blood varies with shear rate. Blood becomes less viscous at high shear rates like those experienced with increased flow such as during exercise or in peak-systole. Therefore, blood is a shear-thinning fluid. Contrarily, blood viscosity increases when shear rate goes down with increased vessel diameters or with low flow, such as downstream from an obstruction or in diastole. Blood viscosity also increases with increases in red cell aggregability.

In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like water, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain when stretched and immediately return to their original state once the stress is removed.

<span class="mw-page-title-main">Thixotropy</span> Change in viscosity of a gel or fluid caused by stress

Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick or viscous under static conditions will flow over time when shaken, agitated, shear-stressed, or otherwise stressed. They then take a fixed time to return to a more viscous state. Some non-Newtonian pseudoplastic fluids show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity. A thixotropic fluid is a fluid which takes a finite time to attain equilibrium viscosity when introduced to a steep change in shear rate. Some thixotropic fluids return to a gel state almost instantly, such as ketchup, and are called pseudoplastic fluids. Others such as yogurt take much longer and can become nearly solid. Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated. Thixotropy arises because particles or structured solutes require time to organize. An overview of thixotropy has been provided by Mewis and Wagner.

<span class="mw-page-title-main">Dilatant</span> Material in which viscosity increases with the rate of shear strain

A dilatant material is one in which viscosity increases with the rate of shear strain. Such a shear thickening fluid, also known by the initialism STF, is an example of a non-Newtonian fluid. This behaviour is usually not observed in pure materials, but can occur in suspensions.

<span class="mw-page-title-main">Rheometer</span> Scientific instrument used to measure fluid flow (rheology)

A rheometer is a laboratory device used to measure the way in which a viscous fluid flows in response to applied forces. It is used for those fluids which cannot be defined by a single value of viscosity and therefore require more parameters to be set and measured than is the case for a viscometer. It measures the rheology of the fluid.

<span class="mw-page-title-main">Shear thinning</span> Non-Newtonian fluid behavior

In rheology, shear thinning is the non-Newtonian behavior of fluids whose viscosity decreases under shear strain. It is sometimes considered synonymous for pseudo-plastic behaviour, and is usually defined as excluding time-dependent effects, such as thixotropy.

<span class="mw-page-title-main">Manfred Wagner</span> German chemical engineer

Manfred Hermann Wagner is the author of Wagner model and the molecular stress function theory for polymer rheology. He is a Professor for Polymer engineering and Polymer physics at the Technical University of Berlin.

<span class="mw-page-title-main">Viscosity</span> Resistance of a fluid to shear deformation

The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity is defined scientifically as a force multiplied by a time divided by an area. Thus its SI units are newton-seconds per square metre, or pascal-seconds.

Rheological weldability (RW) of thermoplastics considers the materials flow characteristics in determining the weldability of the given material. The process of welding thermal plastics requires three general steps, first is surface preparation. The second step is the application of heat and pressure to create intimate contact between the components being joined and initiate inter-molecular diffusion across the joint and the third step is cooling. RW can be used to determine the effectiveness of the second step of the process for given materials.

Biofluid dynamics may be considered as the discipline of biological engineering or biomedical engineering in which the fundamental principles of fluid dynamics are used to explain the mechanisms of biological flows and their interrelationships with physiological processes, in health and in diseases/disorder. It can be considered as the conjuncture of mechanical engineering and biological engineering. It spans from cells to organs, covering diverse aspects of the functionality of systemic physiology, including cardiovascular, respiratory, reproductive, urinary, musculoskeletal and neurological systems etc. Biofluid dynamics and its simulations in computational fluid dynamics (CFD) apply to both internal as well as external flows. Internal flows such as cardiovascular blood flow and respiratory airflow, and external flows such as flying and aquatic locomotion. Biological fluid Dynamics involves the study of the motion of biological fluids. It can be either circulatory system or respiratory systems. Understanding the circulatory system is one of the major areas of research. The respiratory system is very closely linked to the circulatory system and is very complex to study and understand. The study of Biofluid Dynamics is also directed towards finding solutions to some of the human body related diseases and disorders. The usefulness of the subject can also be understood by seeing the use of Biofluid Dynamics in the areas of physiology in order to explain how living things work and about their motions, in developing an understanding of the origins and development of various diseases related to human body and diagnosing them, in finding the cure for the diseases related to cardiovascular and pulmonary systems.

Capillary breakup rheometry is an experimental technique used to assess the extensional rheological response of low viscous fluids. Unlike most shear and extensional rheometers, this technique does not involve active stretch or measurement of stress or strain but exploits only surface tension to create a uniaxial extensional flow. Hence, although it is common practice to use the name rheometer, capillary breakup techniques should be better addressed to as indexers.

Mechanics of gelation describes processes relevant to sol-gel process.

References

  1. ↑ James, David F. "Boger Fluids." http://www.annualreviews.org/doi/pdf/10.1146/annurev.fluid.010908.165125 Retrieved Web. 11 Nov. 2013.
  2. ↑ "David V. Boger." http://www.che.ufl.edu/faculty/boger/ Archived 2015-07-29 at the Wayback Machine Retrieved Web. 11 Nov. 2013.
  3. ↑ Boger, David V. http://ac.els-cdn.com/0377025777800141/1-s2.0-0377025777800141-main.pdf?_tid=35a90d92-50ba-11e3-ae7d-00000aab0f26&acdnat=1384824824_7a3fbc26d2b80b3ee3987bb560b67636 Retrieved Web. 13 Nov. 2013.
  4. ↑ MacSporran, W. C.; Spiers, R. P. (1982). "The dynamic performance of the Weissenberg Rheogoniometer". Rheologica Acta. 21 (2): 184–192. doi:10.1007/BF01736417. S2CID   94082747.
  5. ↑ Wroe, David. http://www.theage.com.au/news/national/300000-boger-fluid-prize-not-on-the-nose/2005/10/04/1128191716871.html Retrieved Web. 11 Nov. 2013.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.